EDIT: Looks like CriPakGUI, the tool I used to extract the cpks, is just doing something wrong here. I tried some other cpk extractors and the extracted files look ok.
I was looking at the files of the game 428: Shibuya Scramble for the Wii. Most of the files are encrypted. But at the end of each file there is a part that is not encrypted. This part seem to be the first 256 bytes of the original file. See:
At 0xC is a pointer (little endian) that points to the end of the encrypted file (0x01D0 + 0x10 (header size maybe) = 0x01E0). The orignial file is a TPL
(image) with the identifier "00 20 AF 30".
Any idea how to decrypt this?